An Excel tool for the parametric assignment of the use classes of the European EN 335 standard, valid for all conditions of use of wood in buildings, is developed. The assignment for the conditions of for outdoor or semi-outdoor use is carried out by using the Scheffer index, while the assignment for the conditions of interior use is carried out based on the humidity classes of the European EN-ISO 13788 standard. The tool also includes the effect of a series of factors that modify the climatic risk of using wood, depending on the conditions of aggravation or reduction of climatic risk due to the effect of local environmental conditions or construction design. The tool has been tested for seven years in Spanish weather conditions and is accompanied by a GIS viewer with the calculation factors to be considered and the direction of the dominant rain winds corresponding to each location.